that is the block heater for the engine, and as for the air tanks the manual should say drain daily but no one including myself does that because the air system has a electrically heated drier between the compressor and the tanks,the cable only drains the wet side of the tanks, both tanks are compartmented the small section is the wet tank to catch condensation or any water that passes the drier, I drain mine everytime I get fuel, by draining them twice a year you will end up with brakes or suspension problems when the wet tanks fill and push water to the main tanks as your suspension and brakes all run off that air, problems from the water freezing up the lines and no air to release brakes or suspension and rusting out of the back side of the brake chambers.
__________________
|